1. Field of the Invention
The present invention relates to a thin film transistor array substrate included in an active matrix driving type display device. More particularly, the present invention relates to a thin film transistor array substrate with enhanced reliability and a method of manufacturing the same.
2. Discussion of the Related Art
With the advent of the information era, the field of displays, which visually display electrical information signals, has rapidly developed. Thus, research into a method of developing ultra-thin and more lightweight flat display devices with lower power consumption is continuously underway.
Examples of such flat panel display devices include a liquid crystal display (LCD) device, a plasma display panel (PDP) device, a field emission display (FED) device, an electroluminescent display (ELD) device, an electro-wetting display (EWD) device, and an organic light emitting display (OLED) device.
Such flat panel display devices necessarily include flat panel display panels to display an image. A flat panel display panel has a structure in which a pair of substrates is adhered opposite each other with a luminescent or polarizing material disposed therebetween.
Among these display devices, in an active matrix display device, which individually drives a plurality of pixels, any one of the pair of substrates may generally include a thin film transistor (TFT) array substrate.
A general TFT array substrate includes gate lines and data lines that cross each other so as to define a plurality of pixel region. A plurality of TFTs correspond to the pixel regions and are formed at the crossings of the gate lines and the data lines.
As an area of a display device increases, resistance of signal lines such as gate lines and data lines may considerably affect power consumption of the display device. Thus, it is necessary to minimize the resistance of the signal lines. For example, at least one of a gate line and a data line may have at least one stacked structure including copper (Cu) so that the at least one thereof has a low resistance.
However, Cu is a metal with high ductility and thus Through Migration of Cu may easily occur. For reference, the Through Migration of Cu is that a horn of Cu occurred from a layer of Cu penetrates an insulating film which covers the layer of Cu along a weak portion of the insulating film.
In particular, when a TFT is of a multi-gate type including an upper gate electrode formed above an active layer and a lower gate electrode below the active layer, defects in the TFT due to the Through Migration of Cu easily occur.
In particular, source and drain electrodes as well as data lines have a stacked structure including the layer of Cu, and the upper gate electrode above the active layer is formed on an insulating film covering the data lines and the source and drain electrodes so as to be insulated from the source and drain electrodes.
In this regard, the source and drain electrodes include at least the layer of Cu, and a height difference due to the source and drain electrodes is formed. Thus, the insulating film on the source and drain electrodes may be formed more weakly in a height change region due to the source and drain electrodes than in the other region and, accordingly, the Through Migration of Cu may easily occur. Due to such Through Migration of Cu, when the upper gate electrode and any one of the source and drain electrodes are short-circuited, the TFT is unable to serve as a switch and bright spot defects occur in the display device and thus there are limitations in enhancing reliability and yield of TFT array substrates.